Born in San Francisco, he made a name for himself in vaudeville, Gallagher with Al Shean to create the act Gallagher and Shean. While the act was successful, the men apparently did not like each other much.

Gallagher first performed with Shean in 1912, but the men broke up in 1914, not performing again until 1920. This latter time, they stayed together until 1925. They had a featured part in the 1922 Ziegfeld Follies, earning a salary of US$1500 a week.

Gallagher suffered a nervous breakdown and entered the Rivercrest Sanitarium in Astoria, Queens, where he died. The final years of his life saw problems with his fourth wife, actress Anna Luther; stress, and alcoholism.